If in the early 1800s you would ask Americans how they saw the geographical future of their country, they would likely include in it the Southwest, still controlled by Mexico. The idea of manifest destiny, that those lands were fated to become American, was the major drive behind the Mexican-American war, which ended in the U.S. army’s occupation of most major cities. Faced with an occupation that Mexico itself had to fund, they had no choice but to cede 500,000 miles of land in Alta and Baja California and New Mexico.

On this day, May 30, in 1848 Mexico ratified the Treaty of Guadalupe Hidalgo, formally transferring the ceded land in the United States. Nicholas P. Trist, the U.S. peace commissioner, on his own initiative added a 13$ million transfer to Mexico to compensate for the loss of land.

The Mexican negotiators did not know this at the time, but Trist was no longer empowered to carry on a negotiation on behalf of the U.S. government. President Polk summoned him back the Washington, D.C. just before the first scheduled meeting to discuss a possible treaty. But Trist chose to stay on and carry on the negotiations through the end.